Composting 101

Adding compost to garden soil improves soil health by providing food for the organisms in the soil that help release nutrients to plants. Organic matter also makes sandy soil hold water better, helps clay soil drain water faster, and buffers soil pH levels.

Although you can add organic matter to the soil in its raw form, such as grass clippings, chopped leaves, hay, straw, pine needles, and peat moss, it's best to compost it first. Finished compost is organic matter that has decomposed into a dark, rich, earthy-smelling material. Use it to mulch trees and shrubs, top-dress the lawn, build up the vegetable or annual flower garden beds, or improve the soil around perennial flowers.

You can buy bulk and bagged compost in many localities, but why not make your own? You can recycle organic yard waste, such as grass clippings and dried leaves, save on the amount of material you send to the landfill, and save money. If you build the pile properly, the soil bacteria goes into a feeding frenzy, and the pile heats up. The end result is rich compost.

Building a Compost Pile

You can build a compost pile in a variety of ways. The simplest technique is to buy or build a 3- to 4-foot wide container. The bins are more visually attractive than large, open piles, and they often compost faster. If you have the room, you can build a free-form pile or series of piles to make lots of fresh compost. Whichever method you choose, the process is the same. You'll be mixing carbon- and nitrogen-rich organic materials with some water to make it heat up and break down. Here are the steps you should follow.

  1. Add a brown layer.
    Start by adding a 4- to 6-inch layer of brown (dry, carbon-rich) materials on the bottom of the container. Good brown materials include dried leaves, hay, and straw.
  2. Add a green layer.
    Add a 2- to 4-inch-thick layer of green (moist, nitrogen-rich) materials on top of the brown. Green materials include fresh grass clippings, vegetable kitchen scraps, and manure. Avoid using any herbicide-treated grass clippings. If you don't have enough green materials on hand, add a cup or two of a granular, high-nitrogen fertilizer, such as alfalfa meal or blood meal.
  3. Moisten.
    Wet each layer as you build the pile to accelerate the composting process. Add enough water for the layers to be moist but not soggy.
  4. Alternate layers.
    Alternate the layers of brown and green materials until you fill the container or bin.
  5. Cover it up.
    Cover the container with a lid or tarp. The cover keeps animals and rain out of the compost. If the pile gets too wet, it won't heat up and break down properly.
  6. Turn it.
    Depending on the weather and season, after a week or two the pile should heat up. The heat indicates that soil microorganisms are breaking down the organic matter in the pile. Once the center of the pile cools, move the outside materials into the center of the pile and the center materials to the outside of the pile with a shovel or garden fork. The pile should heat up again. Continue turning every few weeks.

After a few months, you should have finished compost with a dark color, earthy smell, loose and crumbly texture, and little of the original organic materials visible.

If you want to compost kitchen scraps in winter in a cold climate, try setting up a worm bin composting system. You can place worm bin composters in the basement or even under the kitchen sink. Simply feed the worms fresh kitchen scraps, and they will slowly turn them into worm juice and worm compost. The compost and worm juice (liquid from the compost) are great additions to houseplants and container plants. You can also make your own compost tea from finished compost.

How Much to Use?

Once you've created your compost, you'll need to spread it. How much you use depends on the type of garden. For a new vegetable garden on poor soil, add a 4- to 6-inch layer and turn it into the existing soil before planting. For established vegetable or annual flower gardens, add a 1- to 3-inch layer every spring. Around trees and shrubs, add a 3-inch layer around or beyond the drip line of the plant each spring. On lawns, top-dress with a 1/2-inch layer of compost in fall. Rake it in with an iron rake. While most container gardens use potting soil exclusively, you can add one-quarter compost by volume to add more fertility to the pot.

Information courtesy of the National Gardening Association,